This Mentored Clinical Scientist Development Award (MCSDA) application outlines a program of career development and research to study the interaction between psychobiological and psychosocial factors associated with adolescent major depressive disorder (MDD). The application is aimed, ultimately, at the development of more specific treatment interventions for juvenile depression. The candidate has received preliminary training in EEG sleep in studies with depressed youngsters. The career development and research plans are designed to enable the candidate to develop greater expertise in the area of sleep polysomnography, and to incorporate psychosocial measures in future biological research paradigms. The career development plan includes didactic instruction in sleep physiology, developmental and psychosocial theories of depression, and biostatistical methods for multivariate and longitudinal data. Also included are laboratory experience in quantitative EEG analysis, and the application of sleep and stress paradigms in animal models of depression. A controlled longitudinal investigation is proposed to examine the develop-mental trajectories of adolescents with MDD during the transition to adulthood. The aim of the project is to test a model of two possible pathways to adolescent depression: (1) primarily by means of biological vulnerability (namely, sleep dysregulation); and (2) through susceptibility to psychosocial processes (including life stress). Further, individual differences in inter-action of biological and psychosocial liabilities that may result in their own unique prognostic status in young adulthood will be explored. A better understanding of the role of each of these factors has the potential to lead to more specific treatment and prophylactic interventions with depressed adolescents. The proposed research is unusual in three respects: (1) a community sample of (in contrast to clinically referred) depressed adolescents will be studied; (2) investigator-determined (as opposed to self-report) assessment of life stress will be used, and (3) biological and psychosocial variables will be combined into models tested for their ability to explain differing outcomes among depressed and control adolescents. In addition to furthering the candidate's transition to independent research, the knowledge gained from this study should advance our understanding of this important developmental period as well as etiological factors associated with adolescent depression.